Multi-level semiconductor structures commonly require intermetal dielectric films or layers of high quality and dielectric strength. Dielectric deposition processes for ultra-large scale semiconductor integrated circuits (ULSI) have developed primarily through extensive empirical experimentation. Process simulation tools and computer modelling schemes have evolved to assist in controlling numerous process parameters in attempting to make more predictable the properties of deposited dielectric films as functions of the process parameters involved in the fabrication of such films. It is therefore desirable to understand the deposition processes in order to predict operational ranges and interactions of fabrication parameters that will yield dielectric films with required characteristics.
Conventional tetraethoxysilane (TEOS)--based chemical vapor deposition enhanced by an oxygen plasma discharge is characterized by the complicated dependencies of the silicon dioxide (SiO.sub.2) film deposition rate and film quality upon such factors as the design of the reactor chamber, inlet flow rates of process gases, inlet gas pressure, temperature distribution, plasma excitation power, and the like.
Increasing density of gates in ULSI technology dictates low-temperature processing at many stages of semiconductor fabrication. However, when this requirement applies to the deposition of the SiO.sub.2 from TEOS, a conflict with the process requirements to achieve high film quality can arise. The quality of SiO.sub.2 films can be compromised by the poor stability and impurities incorporated into the film when deposited at low temperatures. The film instability may be caused by high concentration of impurities incorporated into a growing film, and such impurities can degrade reliability of devices fabricated by such low-temperature processes. The sources of these impurities are typically the chemical reactions governing the film formation. As currently understood, SiO.sub.2 film growth is a result of a number of homogeneous and heterogeneous reactions and processes including creation of active precursors from TEOS in a gas phase, and adsorption of these precursors on surface sites. For example, a conversion of remaining ethoxy groups into hydroxyl groups due to elimination of the carbon and hydrogen is considered as a possible limiting step of the entire process. See, for example, D. Dobkin et al, J. Electrochem. Soc. v. 142 pg. 2332 (1995). Many reactions are characterized by the high activation energies that require high temperatures to reach reasonably high SiO.sub.2 deposition rates.
Certain known techniques of low temperature SiO.sub.2 deposition include tetraethoxysilane-based plasma enhanced chemical vapor deposition (PETEOS or TEOS PECVD), and atmospheric pressure CVD (APCVD) Ozone/TEOS deposition. These known techniques rely upon introduction of reactive oxygen species which can react with TEOS and its fragments in the gas phase and in adsorbed layers to produce intermediate species that readily participate in the reaction with resultant formations of siloxane bonds in the SiO.sub.2 layer that deposits at lower temperatures.
Different models for TEOS PECVD have been published with a suggestion that production of atomic oxygen is a rate limiting process to the SiO.sub.2 deposition. See: G. B. Raupp et al, J. Vac. Sci. Tech, B10, pg. 37 (1992). Alternatively, the precursor adsorption is considered as a rate limiting factor. See: n.n. Islamraja et al, J. Appl. Phys., vol 70, pg. 7137 (1991) and J. E. Crowell et al, J. Vac. Sci. Tech, A8, pg. 1864 (1990). The high conformality of SiO.sub.2 films deposited by TEOS PECVD is also explained by the different deposition mechanisms J Appl. Phys., vol 70, pg. 7137 (1991), cited, and P. J. Stuart et al J. Vac. Sci. Tech., All, pg. 2562 (1993). However, TEOS decomposition in the gas phase and on the surface of the growing film is considered as the only way to form the active intermediates responsible for siloxane bond formation.